2004 Kia Optima Door lock button/ key sometimes won't relea

My Kia does not have automatically locking door locks. I see lots of discussion about those failing and people crawling in from passenger side. This is NOT that problem.
My car will unlock all of the doors if you twist the key in the driver's door twice. At least, it should. Sometimes it only unlocks the driver's door.
There is also a button on the door console to unlock or lock all the doors. Again, sometimes it works, sometimes it does not.
I hear a clicking sound whether it works or not.
Doesn't seem to matter if it's warm or cold out. Doesn't seem to matter if the car's warmed up. So I don't think its anything like the mechanism being stiff.
What might I try?